1. Field of the Invention
The present invention relates to a flow rate measuring apparatus for outputting a signal according to a flow rate, for example, to a flow rate measuring apparatus suitable for measuring an intake air flow rate of an internal combustion engine.
2. Description of the Related Art
Conventionally, the following flow rate measuring apparatus is known. The flow rate measuring apparatus is inserted into an apparatus insertion hole provided to an intake pipe so as to be installed therein to measure a flow rate of air passing through the intake pipe (see Japanese Patent Application Laid-open No. 2009-008619 (FIG. 1)).
The flow rate measuring apparatus includes: a base made of a resin, which includes a base main body having a connector formed at a base end portion so as to project to the outside of the intake pipe, and a flange provided so as to radially extend from the base main body to be fitted into the apparatus insertion hole; a plate provided so as to partially overlap the base main body; a flow rate detection element provided on the plate in an exposed manner, for detecting the air flow rate; a circuit board provided on the plate on a side closer to the connector, which includes a control circuit for processing a signal from the flow rate detection element; a housing made of a resin, including a fluid passage groove which forms a measurement passage in cooperation with the plate, and an enclosure portion for enclosing the circuit board; and a cover which closes the enclosure portion to cover the circuit board.
One surface of the plate is bonded to the base main body of the base by an adhesive, whereas the other surface of the plate is bonded to the flow rate detection element, the circuit board, and the housing by an adhesive.
The enclosure portion of the housing is fitted into a concave portion formed in an inner wall surface of the flange of the base, whereas the housing is bonded to the base main body and the plate (see FIG. 16).
In the flow rate measuring apparatus having the above-mentioned configuration, the enclosure portion of the housing is fitted into the concave portion of the base so that the housing is fixed to the base. When vibration is applied to the intake pipe, a so-called cantilever state occurs. In the cantilever state, the flange of the base becomes a fixed end, whereas a distal end of the combination of the plate and the housing becomes a free end. In a certain vibration frequency range, resonance vibration occurs with the flange acting as a base point. As a result, the free end is horizontally deformed about the base point as a center.
In the case of the flow rate measuring apparatus described above, when the enclosure portion is fitted into the concave portion to fix the housing to the base, a clearance is present between the enclosure portion and the concave portion of the base although the clearance is small. Therefore, a margin for the deformation of the base main body is increased by the amount of the clearance. With the deformation of the base main body, the circuit board is also deformed. Then, a repeated stress is generated on a wire which electrically connects the connector and the circuit board to each other. As a result, there is a problem in that fatigue disconnection of the wire is likely to occur.